It has been known for long to provide dental furnaces with control devices which determine and control the exact course of the temperature curve of the dental restoration parts to be fired.
An example of an elaborate control of this type can be taken from DE 35 05 346 A1. In the solution known from this document the liquidus temperature of the molten material is detected by measuring the temperature course of the molten material as exactly as possible when heating power is supplied and by detecting the achieved increases in temperature per heating power supplied.
This solution suggested at that time already shows that it is not sufficient to simply predetermine an exact temperature/time profile for one specific dental furnace; in some cases, the current temperature that actually exists in the interior of the dental restoration part in practice deviates significantly from the furnace temperature.
In practice, the deviation value depends on numerous parameters. Among them are the size, the mass and the shape of the dental restoration parts, but also the material of which they are made, the melting temperature of the material, the specific thermal capacity, the arrangement of the dental restoration parts in the furnace—i.e. to that extent the distance to the heating which is most often arranged in a ring-shaped manner—, the heating rate, the amount of negative pressure in dental firing furnaces operated at negative pressure and the existing pressure exerted on the press blank in press furnaces.
Further parameters, such as ambient pressure and ambient temperature, can also play an important role in sections of the temperature profile already passed through.
In order to pass through the desired temperature as exactly as possible control panels for controlling the furnace have also been developed which serve to show the actual temperature and to symbolically represent the course of the temperature/time diagram. An example hereof can be taken from DE 31 46 391 A1.
When implementing such solutions, however, it turns out again and again that misfirings occurred in spite of careful attention to the specified manufacturer's instructions and settings of the plurality of parameters in a manner adjusted to the material, which means that dental restorations were produced which are of low quality.
Discolorations of ceramic parts can be at least partially compensated for by painting techniques in retrospect. If, however, the dental ceramic used is not fired at the desired temperature and the temperature course stipulated by the manufacturer, the specification of the ceramics is typically not complied with. For instance, lithium disilicate ceramics exhibit good biocompatibility which also involves no or only very limited signs of wear on the antagonist opposite from the dental restoration. If the exact temperature-pressing course is not adhered to, the favorable properties of this ceramic part may not be achieved or only to a reduced extent.
In the case of relatively old ceramic parts, or in the case of zirconium dioxide ceramics, depending on the case of application, brittle fractures resulting in corresponding recourse claims can occur.
In order to further minimize mistakes when firing dental restoration parts numerous suggestions and developments have been undertaken. For instance, attempts have been made to detect the temperature of the products to be fired more exactly, as is known, for instance, from DE 10 2007 035 609 A1. But still there is the need to eliminate or reduce risks in the firing process and the aforementioned problems.